Threads that are steel and epoxy

So I have a spare drill chuck arbor. The first one the vendor sent had the drawbar hole (3/8"-16) threaded off-axis...Not a lot, but enough that I couldn't use the drawbar in the mill.

Not wanting to just trash the bad arbor I epoxied (JB Weld) in a piece of threaded rod, thinking I would cut new threads properly this time. I'm about to cut the new threads, but it got me to thinking...The threads are going to be part steel and part epoxy, being cut across the old threads. Will this still hold up? Should I have bored out to a larger size to fit a steel plug (or larger threaded rod) that would assure the threads would be entirely in steel?

Mike

I'd have sent it back for either a use able one or a refund. Too late now. Advantage of ebay/PayPal, they refund on demand

Hi Duncan. Yeah, I got a replacement. Just hate to trash the bad one if I can get a second arbor out of it.

Is opening the hole out and threading larger an option?

You could then loctite a Threaded Bush in

Jim

YOu could try drilling and tapping it as it is. The amount of epoxy is going to be very minimal, just the bit between the two threads. You might get a little picking up during tapping so proceed with caution and don't force it.

If it doesn't work, then you could go ahead and bore the hole out larger, thread it and screw in a threaded plug, loctite or epoxy it then drill and tap your new mounting hole unmolested in the middle of the new plug.

Bore it out and put a thread insert in ??

Don't know about JB Weld but I have done similar mixed material threads with Devcon metal loaded filler whch worked out OK. But this was basically filling in a Dutch keyway so the original thread was mostly complete and could be used as a guide. Devcon is significantly harder than JB weld and takes threads pretty well itself. My impression is that a thread in the steel filled version is about as strong as one in aluminium.

Keeping the tap straight will not be easy. If there is any significant offset the tap will want to run into the softer JB weld. Serial taps driven under power in the mill is probably the best that can be done i a home workshop. But care an patience with hand taps should get the job done. Preferably with a guide.

As Hopper says the amount of JB weld left should be pretty minimal. Most likely just short bits of male thread and similar part filled female bits. Its likely that these will come unstuck and be dragged out with regular use of the drawbar leaving a very ratty all metal thread behind. Unless you are very lucky your re-tapped thread will not align with the original so the actual tread will be somewhat reminiscent of the spiky efforts on the metal inserts used on cheap furniture where a thread needs to be put into wood to hold a bolt.

Albeit female and rather little more complete. How complete being in the lap of the gods. Could be nearly complete and just a bit slack, could be horrible. Basically are you feeling lucky.

A little inadequate for drawbar threads on an arbor methinks. If the opening threads are poor the drawbar will not insert cleanly and its threads are likely to be damaged.

Sensible thing is to cut your losses, bore it out and loctite a decent threaded bush in.

Clive

Edited By Clive Foster on 01/03/2022 09:40:36

drill and tap as is. is likely to end in a broken tap when the part you glued in moves or jamming the draw bar when it moves later. only safe way is to drill it oversize fit an insert or sleeve. but is it worth it for a piece of junk the cost you nothing

Agreed, after rereading the OP. I think Clive and Martin are right. Trying to retap the same thread but only slightly less out of whack is likely to end up with small bits of thread spiral breaking off and jamming up either the tap at inception or the drawbar later on. Safest bet would be to follow the suggestions of drill/bore it out as far oversize as practical and drill and tap a whole new thread that will remain intact in multiple in and outs of the drawbar.

In order to get the hole concentric with the locations it would have to be bored out to at least the next thread size. Then a threaded blank insert loctited in and preferably pinned across, fooled by drilling and tapping back to size. The thread has to be able to take the tension of the drawbar and torsion implied. Trying to correct it with anything non metallic risks injury at some point when the thread gives way.

I hadn't thought of the tap wanting to follow the softer material, or bits breaking off and jamming the tap. I'll bore it out. I do have some M12 threaded bar, which should do the trick. Thanks gents!

Mike

Since Loctite was mentioned...Is there any reason to prefer Loctite over, say, JB Weld (yes, I have plenty left) for securing the oversize bush/plug/insert?

A 3/8" drawbar would fit a MT2, I would guess, and to get enough diameter in the wall after boring central to take a helicoil, the length would have to be reduced. The helicoil would take up less room than a threaded bush. You would have to make a longer drawbar just for that arbor. It would be easier to bin the arbor and replace it. But be careful, most MT2 arbors have a 10mm thread in them.

Yes JB Weld should be ok in that application. It would only have to stop the insert from screwing out when you undid the draw bar, so no great load on it. And it probably bonds in the same region of strength as Loctite for practical purposes.

In the old days before we had such luxuries, we just put a ring of centre punch marks around the join between the insert and housing, thus "upsetting" the thread and stopping it from screwing out. But today's adhesives are probably more reliable.

You can use treacle as well. In fact I think that is all some of the lower grades of Loctite are. They are sweet to the taste. If you ever worked in a sugar mill (the main industry where I now live) you would find that every nut and bolt on the sugar "liquor" pipework had to be cut off with an oxytorch. Sticky stuff that sugar.

Good to know!

Mike

I'm a bit mystified by this thread. If the OP's arbor is MT2 and its drawbar thread is only slightly skewed then my solution would be to use a tap (same thread and pitch) as the existing thread and manually recut the thread with the tap 'coerced' so its cuts mainly in a direction opposite to the existing skewed thread.

The resulting tapped hole might be a bit sloppy on the drawbar but the drawbar to arbor fixing does not need any great strength.

The suggestions of boring, sleeving or fitting inserts seem out of proportion in relation to the problem.

In any event how does one hold a Morse adapter so that the small end is secure enough to single point bore, yes is possible but is it worth it, (assuming its soft enough to bore)

Ian P

Hi Ian. The arbor is MT3 with 3/8"-16 hole. Coercing the tap would likely break it. Not something I wanted to try. Single pointing the thread is too late now, as the threaded rod is epoxied in place.

I have the JT33 end of the arbor pressed into a drill chuck with a turned bar in it. That will get dialed in with the 4-jaw lathe chuck. The fixed steady will go on the MT3 taper end. Just haven't gotten to it yet.

Yeah, may be a time-waster, but I'm currently unemployed. Also, I'm cheap. Still could be a learning experience, though.

Mike

Now the size has been confifmed as MT3, it gives a much better chance of repair as the small end is just over 3/4" diameter. With a keyed chuck, there should be enough of the front end to hold that in the four jaw. I have cut tangs off and faced and drilled MT's holding the chuck this way.

The thread could be turned / drilled out and tapped M12.

Having Loctied a piece of M12 studding, or bolt into it, it can then be drilled 5/16" diameter and tapped 3/8 BSW (Which is / was the standard drawbar thread for many items )

If you want to maximise concemtricity, hold the work in a four jaw, centralise the taper with a DTi and then use a steady on the taper. There will only be line contact, but that should suffice for the drilling and tapping operations.

Howard.